Electron multiplier



Nov. 12, 1940. w. FLEcHslG ELECTRON MULTIl-"LIER Filed June 17, 1938 Patented Nov. 12, 1940 UNITED STATES ELEc'ritoN MULTIrLIsit i Y Werner Flechsig, `VBerlin-Ch'arlottenbin'g, Germamy, assigner `to the firm of Fernseh Aktiengesellschaft, Zehlendorf, near Berling Germany Appt-zestien June 17.,` lesaseriaine. 214,179

In Germany June 26, 1937 s claims.- `(o1. esc- 175) This invention relates to electron multiplier tubes and particularly to such tubes which employ a series of foraminated electrodes held at increasing potentials,V at which electron multiplication by secondary emission takes place. Such electrodes, as is well known in the art, may consist entirely of a secondary emissive materialsuch as` nickel and others, or may consist of a base metal carrying a layer of high secondary emissivity such as produced by` caesium. These tubes normally comprise a cathode, which may be of the thermionic or photoelectric type, a series of foraminated electrodes held at increasing potentials; and an electron-collecting ande to which the highest potential in the system is applied. In some cases it is desirable to modulate the electron stream in the tube by applying a modulating voltage to `a control grid. The

, control grid can be placed next to the cathode,

thus modulating the primary emission.` It may, however, be desirable to subject the primary current to electron multiplication before modulation. This may be accomplished by inserting a control grid in the path of the electron stream after s veral` stages of vmultiplication When the electron stream` arrives near the control grid, it will have velocity` components of largely varying values. This is becausefcertain electrons arriving at a secondary emissive electrode of the type described will pass through the openings without impacting the solid .portions of the electrode, and .will continue their travel at increased speed. Other` electronswill impact solid portions of the secondary emissive electrode and liberate secondary electrons, which will join the electron stream with a velocity considerably lower than that of the arriving primaries. Under these conditions the effectiveness of a control grid is greatly limited. By no means can 100% modulation be achieved.

It is the object of this` invention toovercome this disadvantage; and to provide an electron multiplier in which a multiplied electron stream can be modulated without distortion.

Broadly considered, this invention provides for division of the electron stream after passing through several stages of multiplication into two components according to the electron velocities. The ratio of the two components into which the electron stream is divided is made in accordance with an applied modulating voltage. The highvelocity component of the electron stream is collected after division without further multiplication. The low-velocity component may be subjected to further multiplication before it is iinal- 1y collected and made use ofvin a work circuit.

The operation ofthe tube may now be explained in detail with the `aid of the drawing wherein the figure is aA View in section of a preferred form "of` my invention. l is a vacuum receptacle housing a thermionic cathode 2, adjacent `to which a series oi foraminated secondary emissive `electrodes 3 are disposed. Modulation of the multiplied electron stream is to take place after the last of` the series of electrodes. At this point the vacuum receptacle is provided with a protrusionlextending at a right angle from the main tube airis.v In this protrusion control grid 5 and a further series of secondary emissive electrodes 5 are located. 4 Control grid 4 is so biased that the 'resulting field will divert secondary electrons liberated at that electrode of series 3 closest to Il towards the control grid, while high-velocity electrons passing through the secondary emissive electrode are not deviated from their initial path but travel past the control grid and finally arrive at a collector 6. i5A maybe preferably given the shape of a` cage, as indicated in the drawing, to prevent 'secondary electrons liberated by the impacting electron stream from re-entering the multiplierfstructure. The low-velocity stream of electrons 'drawn towards control grid fi will be modulated by the modulating voltage applied to this grid, whereupon the modulated electron stream is then subjected to further multiplication by impact upon secondary emissive electrodes. The modulated `electron stream is finally collected at the anode 1. In this manner distortionless modulation of the electron stream can be accomplished.

It is also possible to `.provide a second control grid between the cathode 2 and the first of the secondary emitting electrodes 3. Thus, two modulating voltages canv then be applied, one of which may be a radio-frequency carrier. It is, of course, also possible to provide a photocathode as the primary source of electrons to amplify the primary current and to introduce a carrier frequency at control grid 4,

The idea of the invention can be incorporated also in other electron multiplier structures inasmuch as the secondary emissive electrodes 5 need not be ioraminated, but may be solid, whereby the electron path may have a zigzag or similar shape. It is also possible, of course, to provide for one or several solid secondary emissive electrodes between the cathode 2 and the series of foraminated electrodes 3.

' If the collector 6 is given the shape of a flat plate, care must be taken to assure a low secondary emission ratio, which can be eifected by using a carbonized nickel plate. It is also possible to provide a suppressor grid in front of collecting plate 6.

It may also be preferable, if seen necessary, to carbonize control grid 4 or to provide it with a coat of chromium oxide in order to prevent secondary emission by stray high-velocity electrons.

What I claim is:

1. An electron multiplier comprising a. primary electron source, rst means for multiplying by secondary emission the emission from said primary source, second means located at an angle to said first means for selecting the 10W- velocity component of the multiplied electron stream, said second means including in aligned relation a third means for modulating said lowvelocity-component and fourth means for collecting the modulated 10W-velocity component, and fifth means for collecting the unmodulated high-velocity component of said multiplied electron stream, said fifth means being in alignment with said rst means.

2. An electron multiplier comprising a primary electron source, first means for multiplying by secondary emission the emission from said primary source, second means located at an angle to said rst means for selecting the low-velocity component of the multiplied electron stream, said second means including in aligned relation third means for modulating said low-velocity component, fourth means for multiplying by secondary emission said 10W-velocity component and fifth means for collecting said multiplied modulated low-velocity component, and sixth means for co1- lecting the unmodulated high-velocity component of said rst-named multiplied electron stream, said sixth means being in alignment with said first means.

3. An electron multiplier comprising a cathode, an anode, an electron multiplying stage intermediate said anode and cathode in the path of electron illow from said cathode to said anode, means including an electron-diverting grid located adjacent said path of electron flow for diverting and modulating a low-velocity component of electrons from said path, and means for collecting said modulated 10W-velocity component.

4. An electron multiplier comprising an envelope having a main chamber and an extension chamber therefrom at an angle thereto, a cathode at one end of said main chamber, an anode at the other end of said main chamber, an electron multiplier stage in the path of electron flow from said cathode to said anode, said extension chamber opening into said main chamber at a location intermediate said electron multiplier stage and said anode, means in said extension chamber for diverting a low-velocity component of said electron oW into said extension chamber, and means for collecting said low-velocity component.

5. An electron multiplier comprising an envelope having a main chamber and an extension chamber therefrom at an angle thereto, a cathode at one end of said main chamber, an anode at the other end of said main chamber, an electron multiplier stage in the path of electron flow from said cathode to said anode, said extension chamber opening into said main chamber at a location intermediate said electron multiplier stage and said anode, a grid electrode at the entrance to said extension chamber for diverting and modulating a low-velocity component of said electron ilow, and means in said extension chamber for amplifying and collecting said modulated lowvelocity component.

6. An electron multiplier comprising means for producing a stream of electrons possessing various velocities, electrostatic means for dividing said electron stream into a high-velocity component anda 10W-velocity component, means for modulating said low-velocity component, and means for collecting said modulated low-velocity component, said two last-mentioned means being located in aligned relation at an angle to said first-mentioned means.

7. An electron multiplier comprising means for producing a stream of electrons possessing various velocities, electrostatic means for dividing said electron stream into a high-velocity component and a low-velocity component, means for modulating said 10W-velocity component, means for multiplying said modulated low-velocity component by secondary emission, and means for collecting said last-named component after multiplication, said three last-mentioned means being located in aligned relation at an angle to said first-mentioned means.

8. An electron multiplier comprising a rst electrode assembly including a cathode for producing an electron stream and a plurality of foraminated secondary-emissive electr-odes for multiplying said electron stream, a second electrode assemblyadjacent said rst electrode assembly including a control grid and an anode for diverting a portion of said multiplied electron stream, said second electrode assembly being located at an angle to said rst electrode assembly, and an electron collector in alignment With said rst electrode assembly for collecting the remaining portion of said multiplied electron stream.

WERNER FLECHSIG. 

